Fuel cells utilizing a hydrogen-containing fuel gas to generate electric power are typically arranged to have a stack structure obtained by stacking multiple power generation assemblies via separators (hereafter this may be referred to as ‘fuel cell stack’). Repetition of starting and stopping the operation of the fuel cell stack may cause some defect or flaw in a sealing member located between the power generation assembly and the adjacent separator or may cause distortion of the fuel cell stack, which results in producing a gap between the power generation assembly and the adjacent separator. A fuel gas may be leaked from the defect or the flaw or from the gap.
Sensor-based gas detection is conventionally adopted in fuel cell systems including such fuel cells (see, for example, Japanese Patent Laid-Open No. 2007-46916, No. 2004-179024, No. 2006-19035, and No. 2007-66643).
Detecting deterioration of a fuel cell stack generally requires much time and labor, for example, disassembly prior to a checkup. Especially in a vehicle equipped with fuel cells, it is highly demanded to check the level of deterioration of the fuel cells, which are neither detached from the vehicle nor disassembled but are kept on the vehicle.
This demand is not restricted to detection of a leakage of a fuel gas from the fuel cells but is commonly found in, for example, detecting a leakage of a fuel from any of a gasoline engine, a diesel engine, a hydrogen engine, and a natural gas engine, as well as detecting a leakage of a fuel from production equipment used for manufacturing and accumulating the fuel.